This invention concerns a thin film transistor for use in a flat plate display, and more particularly the source electrode thereof.
Generally, thin film transistors are used as switching elements for flat plate displays because they are characterized by low voltage, low power consumption, light weight and high quality visual reproduction. Such a thin film transistor has a cross-sectional structure as shown in FIG. 3. In producing the thin film transistor, first metal thin film of chromium (Cr) is deposited on a glass substrate 1 to form gate electrode 2, over which a gate insulating layer 3 of a-Si:N, a semiconductor layer 4 of a-si:H, and an ohmic layer 5 of n+ a-si:H are successively laid by plasma-assisted chemical vapor deposition (PACVD).
Subsequently, the semiconductor layer 4 of a-Si:H thin film and the ohmic layer 5 of n+ a-Si:H thin film are etched by photolithography to form a pattern of active regions. Thereafter, contacting hole is formed so as to contact the source electrode 6 with the gate electrode 2. Subsequently, the source electrode 6 and the drain electrode 7 are made of second metal thin film of aluminium (Al). The ohmic layer 5 of n+ a-Si:H thin film remaining in the channel portion between the source electrode 6 and the drain electrode 7 is removed by dry etching, thereby completing the thin film transistor.
Referring to FIG. 2 which illustrates the plane view of a conventional thin film transistor, the gate electrode 2 and the source electrode 6 are formed to cross each other on amorphous silicon layer. Under the gate electrode 2 is formed drain electrode 7, which is in turn connected with picture element electrode 5. In this case, if the gate electrode 2 and the source electrode 6 are contacted with each other at the crossover, the crossing lines of the gate electrode and the source electrode can not be wholly used, thus decreasing the yield rate.